1. Field of the Invention
The present invention relates to a semiconductor wafer-processing method of grinding the rear surface of a semiconductor wafer to form the semiconductor wafer having a desired thickness.
2. Description of the Related Art
A semiconductor wafer having a plurality of semiconductor devices such as integrated circuits and the like formed on the front surface thereof is formed to have a desired thickness by grinding the rear surface thereof and then is dividedly diced into the individual semiconductor devices. In particular, to meet the requirements of downsizing and thickness reduction of electronics, in recent years it has been required that semiconductor devices be formed to have a thickness of as extremely thin as 100 μm or less, or 50 μm or less by efficiently grinding the rear surface of the semiconductor wafer.
If the rear surface of the semiconductor wafer is ground, it is formed with a strain layer with micro cracks having a thickness of about 0.5 μm. This strain layer causes the transverse rupture strength of the semiconductor device to deteriorate. If the semiconductor wafer is formed extremely thin, also the strain layer causes the semiconductor wafer to crack or chip. Therefore, after the rear surface of the semiconductor wafer is ground, the strain layer is removed by polishing, wet etching, or dry etching the rear surface to prevent the degradation in transverse rupture strength (see e.g. Japanese Patent Laid-open No. 2003-173987).
However, for semiconductor wafers formed with a plurality of semiconductor wafers such as e.g. DRAMs having a refresh (data-retaining) function, when the strain layer was removed by polishing, wet etching, or dry etching after grinding of the rear surface, there arose a problem of a degraded data-retaining function. This problem may probably be caused by the following. Metal atoms such as copper or the like contained inside a semiconductor device in a semiconductor fabrication process exist close to the rear surface due to the gettering effect before the removal of the strain layer on the rear surface. However, if the strain layer is removed by polishing the rear surface, the gettering effect is degraded and the metal atoms freely move to the front surface side formed with the semiconductor devices thereon.